US military bosses fear North Korean despot Kim Jong-un is ready to detonate a nuclear bomb that has been placed in a tunnel.

It is believed the secretive state is in the final stages of preparing for its sixth nuclear test.

Reuters

Kim Jong-un, pictured today in Pyongyang, is believed to be on the cusp of triggering the blast

Reuters

North Korea's war threats have sent tremors around the world

AP:Associated Press

Tensions between the US and North Korea are running high

A Voice of America journalist tweeted that US government sources believe North Korea had placed a nuclear device in a tunnel and it could be detonated as early as this weekend.

It comes after Washington-based 38 North, a website that monitors North Korea, said satellite images from Saturday showed vehicles and trailers at the Punggye-ri test site and signs that communications cables may have been laid to a test tunnel.

The think tank said water appears to be being pumped out and was draining downhill "presumably to keep the tunnel dry for monitoring or communications equipment".

It has also been reported Washington is is prepared to launch a preemptive strike on North Korea with conventional weapons against North Korea should it dare test any more nuclear weapons.

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North Korean dictator Kim is apparently determined to become a nuclear warlord

38north.org

Satellite pictures appear to show North Korea is about to test a nuclear device

Yesterday foreign journalists visiting North Korea were told to prepare for a "big and important event" today.

About 200 foreign journalists are in Pyongyang as the country marks the 105th birth anniversary of its founding president Kim Il-sung on April 15, North Korea's biggest national day called "Day of the Sun".

But today the international media were taken to an event where Kim Jong-un opened a prestige housing project.

The Ryomyong Street development is a collection of residential tower blocks of various shapes - round, square and octagonal - with the tallest proclaimed as 70 storeys, or 234 metres, high, and including nearly 5,000 apartments in total.

Tens of thousands of soldiers, officials and citizens packed a plaza from early morning, waiting in the cold Pyongyang spring air for hours before Kim made his entrance, leading a delegation of senior officials and generals on to the platform.

Military tensions are running high, with a US Navy strike group steaming toward the western Pacific in a show of force and North Korea warning of a nuclear attack on the United States at any sign of American aggression.

Meanwhile, US military publication Stars and Stripes reports a USAF aircraft that specialises in detecting radioactive debris after the detonation of a nuclear device has arrived on Okinawa in Japan over the weekend.

Digital

The Air Force WC-135 Constant Phoenix is commonly referred to as a nuke-sniffer

The North Korean nuclear test scare comes just a few weeks after Japan began staging mass evacuation drills after Kim Jong-un test fired missiles and conducted rocket engine tests on intercontinental missiles.

The first exercise of its kind saw civilians young and old scrambling for cover as air-raid sirens wailed away.